There is increasing recognition that performance of a wide spectrum of electronic and optical articles can be enhanced by including a conductive molecule. Examples of such articles include anti-static coatings, films, as well as a variety of electronic implementations. See generally Handbook on Conducting Polymers (Skotheim T. J. ed., Dekker, New York, 1986).
Many types of conductive organic molecules have been reported. For example, U.S. Pat. Nos. 6,172,591; 4,237,441; and 5,378,407 disclose organic polymers with a carbon black or metallic conductive filler.
Organic polymers that are intrinsically conductive have attracted substantial interest. Generally, such polymers include sp2 hybridized carbon atoms that have (or can be adapted to have) delocalized electrons for storing and communicating electronic charge. Some polymers are thought to have conductivities neighboring those traditional silicon-based and metallic conductors. These and other performance characteristics make such conductive polymers desirable for a wide range of applications. See Burroughes, J. H. et al. (1986) Nature 335:137; Sirringhaus, H. et al. (2000) Science, 290, 2123; Sirringhaus, H. et al. (1999) Nature 401: 2; and references cited therein, for example.
Other conductive polymers have been reported. These polymers include a many optionally substituted polypyrrole, polyaniline, polyacetylene, and polythiophene compounds. See EP-A 302 304; EP-A 440 957; DE OS 4 211 459; U.S. Pat. Nos. 6,083,635 and 6,084,040; and Burroughes, J. H., supra.
There is recognition that many conductive polymers can be used to coat a wide range of synthetic or natural articles such as those made from glass, plastic, wood and fibers to provide an electrostatic or anti-static coating. Typical coatings can be applied as sprays, powders and the like using recognized coating or printing processes.
However there is increasing understanding that many prior conductive polymers are not useful for all intended applications.
For example, many of such polymers are not sufficiently conductive or transparent for mans applications. In particular, many suffer from unacceptable conductivity, poor stability, and difficult processing requirements. Other shortcomings have been reported. See e.g., the U.S. Pat. Nos. 6,084,040 and 6,083,635.
There have been attempts to improve some of the prior conductive polymers.
For example, a particular 3,4-polyethylene dioxythiophene (commercially available as Baytron® P from Bayer Corporation, 100 Bayer Rd., Pittsburgh, Pa. 15205-9741 ) has been reported to offer good conductivity, transparency, stability, hydrolysis resistance and processing characteristics. See Bayer AG product literature (Edition 10/97; Order No. A15593, Inorganics Business Group D-51368, Leverkusen, Germany).
More specific Baytron® formulations have been reported for use in specific applications. Illustrative formulations (P type) include CPUD2, CPP103T, CPP105T, CPP 116.6, CPP 134.18, CP 135, CPP 45311, CPP 4531 E3 and CPG 130.6. Baytron® M (commercially available from Bayer Corporation) is reportedly a monomer of poly(3,4-ethylenedioxythiophene) and it has been reported to be useful in the manufacture of organic conductive polymers. Further information relating to using Baytron® formulations can be obtained from Bayer Corporation. See also the Bayer Corporation website at bayerus.com the disclosure of which is incorporated by reference.
Unfortunately, use of many prior mono- and polythiophene formulations has been problematic.
For example, many important Baytron® formulations are provided with significant amounts of water solvent. In particular, many Baytron® P formulations are available as water-saturated colloidal dispersions of the conductive polymer. Typically, a suitable counter ion such as polystyrene sulfonic acid (PSS) is added to the dispersion. There is increasing recognition that many, if not all, Baytron® formulations would be more useful if means existed for exchanging the water solvent wvith one or more other solvents of choice.
There have been limited attempts to develop such solvent exchange methods. Nearly all of the attempts have relied on traditional liquid fractionation and distillation schemes. Such approaches have not been able to exchange the solvent for the water in a way that is effective and reproducible.
Flexible electronic device “writing” or “printing” has attracted much recent attention. An example of such a technique involves dispersing an aqueous and conductive thiophene preparation with an ink-jet printer. Typically, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT/PSS) is employed. See generally Dagni, R. in Chemistry and Engineering, Jan. 1, 2001, pp. 26-27 as well as references cited therein.
However, these writing or printing procedures have suffered for want of an effective and reproducible means of replacing the water with more useful exchange solvents.
There is recognition that many electro-optic devices, such as light emitting diodes (LED's) and photovoltaic cells, require electrically conductive and optically transparent films/coatings as electrode materials. Presently, transparent electrodes in electro-optic devices are made of indium doped tin oxide (ITO) coated glass substrates.
However, most prior ITO layers have suffered from shortcomings.
For example, most prior manufacturing processes involving ITO are cumbersome and costly to perform. An illustration is the need to conduct vacuum deposition in a controlled gas atmosphere. Furthermore, most prior ITO films are brittle, difficult to prepare and manipulate, particularly when used in film formats on large area substrates or flexible substrates. See generally Y. Cao, et al. in Conjugated Polymeric Materials; Opportunities in Electronics, Optoelectronics and Molecular Electronics, NATO Advanced Study Institute, Series E: Applied Sciences, J. L. Bredas and R. R. Chance, Eds., Vol. 82, Kluwer Academic, Holland (1990). See also U.S. Pat. No. 5,618,469 and EPO Patent 686,662.
There is belief that certain conducting polymers and coatings may be qualified for some organic light emitting diode (OLED) applications. Briefly, OLED's are display compositions based on sandwiching deposited organic molecules or polymers between two electrodes. Light emission or luminescence occurs when charged carriers associate with the electrodes recombine and emit light. See U.S. Pat. No. 5,904,961, for instance.
More specifically, a typical OLED includes a metal cathode, electrode transport layer (ETL), organic emitters, the HIL, an ITO anode and glass substrate. Light output passes through the glass substrate.
Electrically conductive and optically transparent coatings have been made with polyaniline (PANI) (U.S. Pat. No. 5,618,469) and PEDOT/PSS polymer dispersion (Eur Patent 686662).
However, many of the prior coatings have recognized drawbacks particularly in relation to OLED applications.
As an example, many have limitations in manufacturing practical electro-optic devices. In particular, it is well known that many PANI systems are not stable. Performance degrades over time. Although there is some understanding that performance of PEDOT:PSS-based devices are stable, many prior PEDOT:PSS polymers are aqueous based. Fabricating PEDOT:PSS coatings onto ITO coated substrates requires cumbersome manufacturing processes. Further, the hydrophilic nature of the PEDOT:PSS system attracts moisture, even through the protective moisture barrier. This characteristic has several disadvantages including premature failure during use.
It would be desirable to have coating and related compositions that are easy to make and use. It would be especially desirable to have solvent-exchanged PEDOT:PSS compositions as well as methods for making and using same that exhibit low resistivity and are suitable for OLED use.